The present invention relates to a method and an analyzer for analyzing a minute foreign substance present on the surface of a planar sample such as e.g., a silicon wafer for semiconductor element or an insulating transparent substrate for liquid crystal display element, as well as a process for semiconductor elements and liquid crystal display elements by use thereof. More specifically, the invention relates to a method and an apparatus, and semiconductor and liquid crystal display elements by use thereof, in which a minute foreign substance is detected by a particle test unit whose coordinate system is predefined, and by linking the identified position of the minute foreign substance with the coordination system of an analytical unit, it is possible to easily analyze, test and evaluate the identified minute foreign substance.
Analyzers referred to as here mean analyzers for investigating the color tone, stereoscopic image, elemental analysis, chemical structure, crystalline structure and the like by irradiating energy such as light, X-ray, electro-magnetic wave, and various corpuscular beams including electron, neutral chemical species (atom, molecule and such others), ion and phonon to the surface of a sample and detecting a secondary corpuscular beam absorbed or radiated due to the interaction with the sample, or treating the surface of a sample, and include units such functions as analysis, test, estimation and treatment, represented by, for example, Metallographical Microscope, Laser Microscope, Probe Microscope, Inter-Atomic Force Microscope (hereinafter, referred to as AFM), Scanning Tunnel Microscope (hereinafter, referred to as STM), Magnetic Force Microscope (hereinafter, referred to as MFM), Scanning Electron Microscope (hereinafter, referred to as SEM), Electron Probe Micro-Analyzer (hereinafter, referred to as EPMA), X-ray Photoelectron Spectrometer (hereinafter, referred to as XPS), Ultraviolet Photoelectron Spectrometer (hereinafter, referred to as UPS), Secondary Ion Mass Spectrometer (hereinafter, referred to as SIMS), Time of Flight-SIMS (hereinafter, referred to as TOF-SIMS), Scanning Auger Electron Spectrometer (hereinafter, referred to as SAM), Auger Electron Spectrometer (hereinafter, referred to as AES), Reflection High Energy Electron Diffraction Spectrometer (hereinafter, referred to as RHEED), High Energy Electron Diffraction Spectrometer (hereinafter, referred to as HEED), Low Energy Electron Diffraction Spectrometer (hereinafter, referred to as LEED), Electron Energy-Loss Spectrometer (hereinafter, referred to as EELS), Focused Ion Beam Instrument (hereinafter, referred to as FIB), Particle Induced X-ray Emission (hereinafter, referred to as PIXE), Microscopic Fourier Transfer Infrared Spectrometer (hereinafter, referred to as Microscopic FT-IR) and Microscopic Raman, as well as observation units, analytical units, test units and estimation units.
The yield in the production of very highly integrated LSI, represented by 4M bit- and 16M bit-DRAM is said to depend almost primarily on defects originating in wafer-adhered foreign substances.
That is because, with finer pattern width, foreign substances of minute size adhered to a wafer in the production process of the previous step, though having so far not been out of the question, becomes the source of pollution. Generally, the size of such minute foreign substances to come into question is said to be on the order of several tenth of the minimum wiring width of very highly integrated LSI to be manufactured, and accordingly minute foreign substances of 0.1 xcexcm level are the object of examination in 16M bit-DRAM (minimum wiring width 0.5 xcexcm). Such minute foreign substances form contaminants and cause disconnection or short of a circuit pattern, greatly leading to the occurrence of faults and a decrease in quality and reliability. Thus, it is a key point to the promotion of yield to grasp and control the actual condition of adhesion and the like of minute foreign substances by accurate measurement and analysis.
As means for this operation, there have conventionally been employed particle test devices capable of detecting the location of a minute foreign substance on the surface of a planar sample, such as silicon wafer. The conventional particle test devices include IS-2000 and LS-6000 available from Hitachi Denshi Engineering Ltd.; Surfscan 6200 available from Tencor, USA; WIS-9000 available from Estek, USA or the like. Meanwhile, on the measuring principle employed for these particle test devices and device configuration for implementation thereof, detailed description is seen, for example, in a literature entitled xe2x80x9cAnalysis/Estimation Technique for High-Performance Semiconductor Processxe2x80x9d, pp.111-129, edited by Handotai Kiban Kenkyukai (Semiconductor Substrate Research Group), Realize Ltd.
FIG. 8 shows a display screen of CRT displaying the results measured by using a particle test device LS-6000 for minute foreign substances (0.1 xcexcm or larger) present on an actual 6-inch silicon wafer. That is, this display screen indicates only the approximate position, the number of foreign substances for each size and the distribution of grain sizes. The circle shown in FIG. 8 represents the outer periphery of a 6-inch silicon wafer and points present in the circle correspond to the respective locations of minute foreign substances. Incidentally, a particle or a foreign substance described here means any different portion such as a concave, convex, adhered particle or defect, which generates a scattering (irregular reflection) of light.
As seen also from FIG. 8, however, the information obtained from a conventional particle test device relates only to the size and location of a minute foreign substance present on the surface of such a sample as silicon wafer, and consequently does not permit one to identify an actual state of the relevant minute foreign substance, such as what it is.
As one example, FIG. 4 shows the basic configuration of a conventional metallographical microscope with an actuator, one example of conventional metallographical microscope with a positioning function employed for the detection of a minute foreign substance as observed in the IC testing microscopic instrument MODER: IM-120 available from Nidec Co. Ltd. In FIG. 4, a sample of silicon wafer 2 is placed on an x-y actuator 1 having a coordinate system roughly linked with that of a particle testing device. The foreign substance 7 detected by the particle testing device is so arranged as to be conveyed to the visual field of a metallographical microscope 3 or the vicinity thereof on the basis of the positional information about the foreign substance obtained from the particle testing device. Hereinafter, the testing procedure and tested results for testing a foreign substance 7 present on the surface of a planar silicon wafer by using a conventional metallographical microscope equipped with actuator.
First, with a plurality of slightly stained mirror-surface ground silicon wafers 2 (CZ (plane orientation: 100) 6-inch diameter silicon wafer, available from Mitsubishi Material Silicon) is put on a particle test device (Surfscan 6200, available from Tencor Ltd., USA), the approximate size and the approximate location of a foreign substance present on the silicon wafer 2 are observed. At random positions on the silicon wafer 2, there were about 800 foreign substances in 0.1-0.2 xcexcm level of diameter, about 130 foreign substances in 0.2-0.3 xcexcm level of diameter, about 30 foreign substances in 0.3-0.4 xcexcm level of diameter, about 13 foreign substances in 0.4-0.5 xcexcm level of diameter, and about 15 foreign substances in 0.5 xcexcm or more level of diameter. The coordinate system in Surfscan 6200 is so defined that, letting the x- and y-axes (or y- and x-axes) be the direction in contact with the orientation flat (hereinafter, referred to as xe2x80x9coriflaxe2x80x9d) and its vertical direction in the surface of a wafer, respectively, three points or more of the outermost, except for the part of orifla, are measured and the center position (0, 0) of the wafer is determined by calculating the measured coordinates with the formula of a circle or ellipse.
Next, a conventional metallographical microscopic is employed, in which by letting the x- and y-axes (or y- and x-axes) be the direction in contact with the orifla and its vertical direction in the surface of a wafer, respectively, measuring three points or more of the outermost, except for the part of orifla, and applying the formula of a circle or ellipse to the measured coordinates, the center position of the wafer is determined in the form of (0, 0). After setting a silicon wafer 2 on an x-y actuator 1, an attempt was made to observe foreign substances of individual sizes with a metallogical microscope 3 by operating an x-y actuator on the basis of the positional information about the foreign substance obtained from the particle test device (estimated and observed with the magnification of an eyepiece fixes to 10 and that of an objective varied to 5, 20 and 50).
As a result, foreign substances of 0.4-0.5 xcexcm level diameter could barely be detected as dark points in the case of using an objective of 5 magnitude in the metallographical microscope and those of smaller level diameter could hardly be detected. More specifically, all those of 0.4 xcexcm or larger level diameter could be detected. On the other hand, in the case of using an objective of 50 magnitude, a foreign substance of 0.2-0.3 xcexcm level diameter could rarely be detected as a dark point, but hardly any foreign substance of smaller level diameter could be detected. Thus, to examine the cause, the deviated amounts of coordination in this case were surveyed using a plurality of check-patterned wafers, which revealed that there were deviated amounts of about (xc2x1250 xcexcm, xc2x1250 xcexcm) relative to the original position or the center position of the wafer and any point definable in the wafer in the representation of x-y coordinates.
Meanwhile, the visual field for an objective 5 of magnitude the device used at this time was about 1500 xcexcm "PHgr", whereas that for an objective 50 of magnitude was only about 150 xcexcm "PHgr".
That is, the reason why many foreign substances of 0.2-0.3 xcexcm level diameter could be selected for an objective of 50 magnitude was found to be that the deviation relatively exceeded the extent of visual field of a microscope due to a change in magnitude from 5 to 50, a high magnitude, and a foreign substance of 0.2-0.3 xcexcm level diameter in question was not included within the visual field of an existing device.
For this reason, it becomes necessary to identify the actual conditions of individual foreign substances through a direct observation or composition analysis by using an appropriate analysis device such as SEM. However, because of being defined in the device coordinate system of a particle test device, locations of individual foreign substances on a wafer do not always coincide with device coordinates of other analysis devices than the particle test device such as SEM. In addition, in setting such a sample as wafer on other analysis devices than the particle test device such as SEM, a coordinate deviation error accompanying a new setting cannot be avoided from occurring. Thus, it is necessary in identifying the actual condition of minute foreign substances to link the device coordinate system of a particle test device with that of a different analysis device such as SEM from the particle test device with high accuracy.
Accordingly, device coordinate systems were investigated for individual particle test devices and different analysis devices such as SEM from the particle test devices. As a result, it was found that the x-y coordinate system is adopted in almost all devices. In determining the coordinate axes and the origin position of each device for a wafer as sample to be measured, there is employed (1) a method for defining the direction of a wafer being in contact with the orifla as the x-axis (or y-axis), its vertical direction in the plane of a wafer as the y-axis (or x-axis) and the interceptions of the y-axis with the outermost periphery of the wafer and with the x-axis respectively as (0, y) and as (0, 0) (cf. FIG. 9(a)), or (2) a method for defining the direction of a wafer being in contact with the orifla as the x-axis (or y-axis), its vertical direction in the plane of a wafer as the y-axis (or x-axis) and the center coordinate of the wafer as (0, 0) by measuring three sample points or more of the outermost circumference and applying the formula of a circle or ellipse to the measured coordinates (cf. Figure (9)b).
In these methods, however, the defined coordinate systems themselves are diverse because the function employed in the definition of coordinate system differs with individual devices or because the number of sample points differs with individual devices. Furthermore, on account of stage error intrinsic in an x-y stage, dependent on the stage accuracy of each device (an actual x-y stage comes to have a somewhat distorted coordinate system relative to the ideal x-y stage as shown in FIG. 3 and this means a differential ei) or an indefinite individual error based on the peculiarity of each device, a deviation occurs without fail in the coordinate axes and origin position of a device coordinate system for a conventional simple xe2x80x9ccoordinate linking method by inputting the positional information about minute defects or foreign substances detected by a particle test device to the coordinate system of a different analysis device such as SEM from the particle test devicexe2x80x9d. In other words, it is required in examining a minute substance to elevate the magnitude, but the visual field of a test region or analysis region becomes narrower with increasing magnitude.
Thus, at the analyzable magnitude for minute foreign substances of an analysis device, it becomes impossible to set a minute defect or substance within the visual field of the device at that time. That is, it is required in examining a minute substance to elevate the magnitude, but the visual field of a test region or analysis region becomes narrower with increasing magnitude.
Then, deviations of coordinates occurring for the above reason were examined for various device by using a plurality of check-patterned wafers. It was found that, even between well accurate devices (particle test device IS-2000 available from Hitachi Denshi Engineering K.K. and length measuring SEM S-7000 available from Hitachi Ltd.), there were deviated amounts of about (xc2x1100 xcexcm, xc2x1100 xcexcm) relative to the origin position or the center position of the wafer and any point definable in the wafer in the representation of x-y coordinates. Accordingly, in analyzing and estimating a minute foreign substance situated at any position on a wafer detected by a particle test device by using a different analytical device from the particle test device, observation or analysis and estimation of the minute foreign substance must be carried out by certain methods of such as magnifying the relevant portion after executing observations in an area (200 xcexcmxc3x97200 xcexcm=40,000 xcexcm2, visual field of the SEM at a 500 magnitude) covering the extent of above (xc2x1100 xcexcm, xc2x1100 xcexcm) centered at a position on which a foreign substance detected by the particle test device is presumed to be present and ensuring the position of the minute foreign substance. Thus, a fairly long period of time is required.
For intuitively grasping what size relation this area has to a minute foreign substance, an attempt was made to examine the presumably detectable size of a minute foreign substance by calculating the detectable extent (area) one pixel of the CCD camera occupies on the assumption that a CCD camera of 1,000,000 pixels regarded at present as a relatively high-resolution CCD camera was employed for observation. The detectable area that one pixel occupies under the above conditions was calculated to be 0.04 xcexcm2 (40,000 xcexcm2÷1,000,000=0.2 xcexcmxc3x970.2 xcexcm). On the other hand, since it is difficult to discern an object of smaller size than one pixel, the detectable limit of minute foreign substances proves to be 0.04 xcexcm2 (0.2 xcexcmxc3x970.2 xcexcm). That is, it is found difficult to directly detect a foreign substance having a projected area of smaller than 0.04 xcexcm2 (about 0.2 xcexcm in diameter) by using a CCD camera of 1,000,000 pixels, and extremely difficult to identify the position of the minute foreign substance. Still less, it is nearly impossible to identify the position of a minute foreign substance, 0.2 xcexcm or smaller in diameter.
From this, it is deduced generally difficult to identify the position of a minute foreign substance, 0.2 xcexcm or smaller in diameter conventionally detected by a particle test device and directly observe or estimate the minute foreign substance by linking the minute foreign substance with the device coordinate system of a different analytical device such as SEM from the particle test device based on the device coordinate system of the particle test device.
For solving such problems, it is an object of the present invention to provide a minute foreign matter analysis method and device wherein the observation, analysis and estimation of minute foreign matter is permitted by employing a means for linking the device coordinate system of a particle test device with that of a different analytical device such as SEM from the particle device with by far higher accuracy.
It is another object of the present invention to provide a process for a semiconductor element or liquid crystal display element wherein the yield and reliability of a semiconductor element or liquid crystal display element are promoted by testing and analyzing a minute foreign substance in the step of manufacturing a semiconductor element or liquid crystal display element through the above analytical method.
The minute foreign substance analysis method as set forth in claim 1 is a method comprising the steps of: determining the position of a minute foreign substance on the surface of a sample in a particle test unit; transferring said sample onto a coordinate stage of an analysis unit; inputting the position determined by said particle test unit for the minute foreign substance to the coordinate stage of the analysis unit; and analyzing the contents of the relevant minute foreign substance wherein at least one of the unit coordinate to be employed in said particle test unit and the unit coordinate to be employed in said analysis unit is previously measured using a standard wafer with a relatively positioned dot arrow provided on the surface to determine an error of the above unit coordinate system and the unit coordinate system of the above particle test unit and that of the above analytical unit are linked with each other by correcting the error relative to the above unit coordinate systems.
In correcting the unit coordinate by using the above standard wafer, it is preferable for minimizing the error to employ the same standard wafer both for the particle test unit and for the analytical unit.
The minute foreign matter analysis method as set forth in claim 3 is a method comprising the steps of: determining the position of a minute matter on the surface of a sample in a particle test unit; transferring said sample onto a coordinate stage of an analytical unit; inputting the position determined by said particle test unit to the coordinate stage of the analysis unit; and analyzing the contents of the relevant minute foreign substance; wherein the relative positional relation between the dots on the unit coordinate system is determined by detecting the positions of dots on a standard wafer in said particle test unit, the relative positional relation between the dots on the unit coordinate system is determined by detecting the positions of dots on said standard wafer in said analytical unit, and the unit coordinate systems of said both units are linked with each other by comparing the respective relative positional relations of said both units.
In the above standard wafer, since the respective dots of said dot array having a relative positional relation are provided randomly and the positional relation between the respective dots is accurately grasped, the formation of dots is easy.
In the above standard wafer, since the respective dots of said dot array having a relative positional relation are determined by a function defined digitally, the correction of the unit coordinate can be treated using the digitally defined function and thus is easy.
Since the respective dots of the above dot array are provided at least for every certain angle on a circle or for every certain interval on a rectangular-coordinate axis, the correction of the unit coordinate can be treated more easily.
In the above dot array, a set of dots comprises dots having different diameters and accordingly it becomes possible to distinguish whether a set of dots is a variation due to pollution or an original set as intended even if a standard wafer is polluted by foreign substances of any sizes, because the diameters and arrangement of individual dots in an array of dots used for the standard wafer are known. In addition, since a set of dots is formed, information as a measure on a scale can be given to an array of dots.
The above sample may be a semiconductor element in an intermediate step of production or a semiconductor wafer during the forming of said element.
The above sample may be a liquid crystal display element in an intermediate step of production or an insulating transparent substrate during the forming of said element.
The minute foreign substance analytical unit according to the present invention is an analytical unit for placing a sample on a stage after the position of a minute foreign substance in the sample is detected by a particle test unit and analyzing the minute foreign substance, additionally comprising: means for finding a variation tendency of the total error, forming the whole error of said analytical unit by using the relative positional relation of dots on a standard wafer; and means for executing a coordinate correction by subtracting the total error from the unit coordinate based on the variation tendency of said total error.
The above means for finding a variation tendency may comprise means for measuring the position of each dot and determining an error from its true value and means for computing the total error of said unit from said errors of measured positions on the basis of a function defined digitally in possession of each dot of said standard wafer.
The particle test unit according to the present invention is a particle test unit for detecting a minute foreign substance on a sample, additionally comprising: means for finding a variation tendency of the total error forming the whole error of said particle test unit by using the relative positional relation of dots on a standard wafer; and means for executing a coordinate correction by subtracting the total error from the unit coordinate based on the variation tendency of said total error.
The above analytical units in the above each analytical method or the above analytical units may be at least one type selected from a group comprising; scanning electron microscope, metallographical microscope, scanning laser microscope, IR microspectroscope for analyzing the chemical structure, Raman microspectroscope, photoluminescence unit for fluorescent spectroscopy, electron beam probe microanalyzer for surface trace element analysis, Auger electron spectrometer, electron energy-loss spectrometer, secondary ion mass spectroscope, time of flight mass spectrometer, particle induced X-ray spectrometer, reflection high energy electron diffraction spectrometer for crystal analysis, focused ion analyzer for surface treatment, X-ray photoelectron spectrometer for chemical structure analysis, UV photoelectron spectrometer, scanning probe microscope, interatomic force microscope, scanning tunnel microscope and magnetic force microscope.
The process for a semiconductor element according to the present invention is a process for a semiconductor element comprising steps including at least the cleansing step, the film forming step, the exposure step, the etching step, the ion injection step, the diffusion step and the heat treatment step, wherein at least one step of said all steps is accompanied by test steps and at least one of said test steps is for the purpose of analyzing a minute foreign substance in accordance with the method as set forth in claim 1 or by using the unit as set forth in another claim.
The process for a liquid crystal display element according to the present invention is a process for a liquid crystal display element comprising the steps of: pasting a TFT substrate with at least a thin-film transistor and a pixel electrode provided on an insulating transparent substrate and an opposed substrate with at least an opposed electrode provided on an insulating transparent substrate at their peripheries together while keeping a fixed gap; and injecting liquid crystal material into said gap; wherein at least one step of the cleansing step, the film forming step, the exposure step, the etching step, and the ion injection step, constituting the production step of said TFT substrate or said opposed substrate is accompanied by test steps and at least one of said test steps is for the purpose of analyzing a minute foreign substance in accordance with the method described in claim 1 or by using the unit as set forth in another claim.
According to the minute foreign substance analytical method as set forth in claim 1, since the unit coordinate(s) of a particle test unit and/or analytical units is (are) corrected by using a standard wafer with a relatively positioned dot array provided on the surface, the total error equal to the sum of the stage error potentially possessed by the unit coordinate(s) and indefinite individual errors originating in peculiarities of the respective units can be effectively corrected. Thus, the position of a minute foreign substance present on a sample can be accurately identified on the basis of a relative positional relation of individual dots (hereinafter, referred to as scale) in a standard wafer and the place of the minute foreign substance detected by a particle test unit can be immediately set up in the visual field of an analytical unit even if the respective coordinate systems have potential errors between different units, so that analysis can be easily carried out.
According to the analytical method as set forth in claim 2, since correction of both units is made by using one and the same standard wafer, the unit coordinate systems can be conformed to the same standard between both units and can be completely linked with each other.
According to the analytical method as set forth in claim 3, since the relative positional relation between the dots of a standard wafer and the unit coordinates is determined in each of a particle test unit and an analytical unit, and the unit coordinate systems of both units are linked with each other by comparing the respective relative positional relations for both units, it is unnecessary to correct the unit coordinate separately in each unit, the unit coordinate systems are linked with each other between both units and the place of the minute foreign substance detected by a particle test unit can be immediately set up in the visual field of an analytical unit, so that analysis can be easily carried out.
According to the analytical method as set forth in another claim, since the dot array of a standard wafer is provided at random, production of a standard wafer is easy, whereas the relative positional relation between the respective dots is accurately grasped, so that correction of each unit coordinate and linage between both unit coordinates can be easily carried out.
According to the analytical method as set forth in another claim, since the dot array of a standard wafer is determined by a digitally defied function, the total error of each unit can be determined by computation, so that correction of each unit coordinate and linage between both unit coordinates can be easily carried out.
According to the analytical method as set forth in another claim 6, since the respective dots of a dot array are provided for every certain angle on a circle or for every certain interval on a rectangular-coordinate axis, each coordinate in the direction of rotation and the directions of the x- and y-axes can be more easily corrected. Incidentally, if the relative positional relation between individual dots is known, any discrete mathematical definition will do.
According to the analytical method as set forth in another claim, since the respective dots of a dot array employed for the scale of a standard wafer comprise a set of dots having different diameters, it is possible to distinguish whether a set of dots is a result of noise due to pollution or an original set of dots as intended on the standard wafer, even if a standard wafer should be polluted by foreign substances of any sizes, by making sure of the diameters and arrangement of individual dots in an array of dots used for the standard wafer and accordingly it is facilitated to read a coordinate, so that a strict correction can be carried out using a standard wafer. In addition, since a set of dots is formed, information as a measure on a scale can be given to an array of dots.
According to the analytical method as set forth in another claim, since minute foreign substances of a semiconductor wafer in an intermediate step of production can be analyzed, the cause of faults in the production step of a semiconductor element can be analyzed.
According to the analytical method as set forth in another claim, since minute foreign substances of the insulating transparent substrate during the formation of a liquid crystal display element can be analyzed, the cause of faults in the production step of a liquid crystal display element can be analyzed.
According to the method or device as set forth in another claim, surface shape, element, chemical structure, crystalline structure, etc., of minute foreign substances can be analyzed, and also, surface treatment can be performed by selecting analytical unit.
According to the particle test unit and the analytical unit as set forth in another claims, since means is provided for correcting the total error potentially contained in the unit coordinate system based on the scale of the standard wafer, it is possible to decrease the affect of the total error potentially contained in the particle test unit and/or the analytical unit, the position of minute foreign substances containing error detected by the particle test unit is linked accurately to the unit coordinate system of the analytical unit, and the minute foreign substance can be easily set within the field of view of the analytical unit.
According to the analytical unit as set forth in another claim, the means for finding a variation tendency comprises means for determining an error of each dot and means for computing the total error, the total error of each unit can be simply determined.
According to the process for semiconductor elements as set forth in another claims, since the status of a minute foreign substance on the surface of a wafer can be examined at any time during the production step by a sampling test or a total test, the circumstances of occurrence or the cause of occurrence of a minute foreign substance in the production step can be known and be fed back to the production step. As a result, demerits due to minute foreign substances can be minimized even in VLSI where wiring is on the order of submicron, thereby promoting the yield and the reliability as well.
According to the process for liquid crystal elements as set forth in another claims, since the status of a minute foreign substance can be grasped during the forming step of. thin-film transistors, signal wiring or the like, accidents such as break down of a wire even in a liquid crystal element of fine wiring accompanied by a more highly miniaturization can be prevented so that the yield and the reliability of liquid crystal elements can be promoted.